diff --git a/src/bn/mod.rs b/src/bn/mod.rs
index cc64d8cd..fddd5703 100644
--- a/src/bn/mod.rs
+++ b/src/bn/mod.rs
@@ -45,6 +45,7 @@ extern {
     fn BN_exp(r: *mut BIGNUM, a: *mut BIGNUM, p: *mut BIGNUM, ctx: *mut BN_CTX) -> c_int;
     fn BN_mod_exp(r: *mut BIGNUM, a: *mut BIGNUM, p: *mut BIGNUM, m: *mut BIGNUM, ctx: *mut BN_CTX) -> c_int;
     fn BN_mod_inverse(r: *mut BIGNUM, a: *mut BIGNUM, n: *mut BIGNUM, ctx: *mut BN_CTX) -> *const BIGNUM;
+    fn BN_mod_word(r: *mut BIGNUM, w: c_ulong) -> c_ulong;
     fn BN_gcd(r: *mut BIGNUM, a: *mut BIGNUM, b: *mut BIGNUM, ctx: *mut BN_CTX) -> c_int;
 
     /* Bit operations on BIGNUMs */
@@ -232,6 +233,12 @@ impl BigNum {
         }
     }
 
+    pub fn mod_word(&self, w: c_ulong) -> c_ulong {
+        unsafe {
+            return BN_mod_word(self.raw(), w);
+        }
+    }
+
     pub fn checked_gcd(&self, a: &BigNum) -> Result<BigNum, SslError> {
         unsafe {
             with_bn_in_ctx!(r, ctx, { BN_gcd(r.raw(), self.raw(), a.raw(), ctx) == 1 })